In manufacturing electronic devices, there is performed a process of forming an opening such as a hole, a trench at a region of silicon oxide (SiO2). In such a process, a target object is exposed to a plasma of a fluorocarbon gas and, thus, the region of silicon oxide is etched, as disclosed in U.S. Pat. No. 7,708,859.
There is known a technique for selectively etching a first region of silicon oxide with respect to a second region of silicon nitride. A SAC (Self-Aligned Contact) technique is known as an example of such a technique. The SAC technique is disclosed in Japanese Patent Application Publication No. 2000-307001.
The target object as an object to be processed by the SAC technique includes a first region of silicon oxide, a second region of silicon nitride, and a mask. The second region is formed to have a recess. The first region is formed to fill the recess and cover the second region. The mask is provided on the first region and has an opening provided over the recess. As disclosed in Japanese Patent Application Publication No. 2000-307001, in the conventional SAC technique, a plasma of a processing gas containing a fluorocarbon gas, an oxygen gas and an inert gas is used to etch the first region. By exposing the target object to the plasma of the processing gas, a portion of the first region which is exposed through the opening of the mask is etched. As a consequence, an upper opening is formed. Further, by exposing the target object to the plasma of the processing gas, a portion surrounded by the second region, i.e., the first region in the recess, is etched in a self-aligned manner. Accordingly, a lower opening continuous to the upper opening is formed in a self-aligned manner.
In the above conventional technique, as the etching of the first region proceeds, an opening of the mask and/or an opening formed by etching the first region are narrowed by the deposit originated from fluorocarbon and this may result in blockage of the openings. As a result, the etching rate of the first region is decreased and the etching of the first region may be stopped in some cases.
Therefore, it is required to etch the first region of silicon oxide with respect to the second region of silicon nitride while preventing blockage of the openings.